There's no shortage of deadlines in 2015 that will put the national media spotlight on Capitol Hill, even as much of the attention is on shooting ranges, ballrooms and diners in early presidential states.

And for what's likely to be four Republican senators making runs for the White House and their advisers, these moments will be an opportunity to distinguish themselves from fellow legislators — and perhaps for the candidates running from governor's mansions or the business community.

The administration's negotiations with Iran over that country's nuclear program are in the spotlight, and the Senate has legislation set to advance that would give Congress a say in any final agreement. With June 30 set as the anticipated deadline for reaching a final agreement based on the recently announced framework, the legislation likely sets up a foreign policy debate ahead of the August recess.

Here are a few of the other deadlines presidential candidates will need to mark on the calendar:

Patriot Act Section 215 and other provisions of the law governing government surveillance powers are up for renewal at the end of May, and the administration has said without it, the intelligence community would be unable to continue bulk collection of telephone-related information.

"If Section 215 sunsets, we will not continue the bulk telephony metadata program," National Security Council spokesman Ned Price said last month, and there's been no change in that position since.

Among presidential contenders, Sen. Rand Paul, R-Ky., seems sure to have an out-sized voice in this debate, even though he drew some criticism last year for voting against an overhaul championed by Democratic Sen. Patrick J. Leahy, D-Vt.

"Warrantless searches of Americans' phone and computer records are un-American and a threat to our civil liberties," Paul said at his campaign announcement in Louisville and throughout his tour of early states. "I say that your phone records are yours."

Highway Cliff At the same time surveillance provisions are set to lapse, the government will run out of money for funding surface transportation programs under current law. Many Republicans still view highway infrastructure a key federal function, though. Paul last week teamed up with Environment and Public Works ranking member Barbara Boxer, D-Calif., to introduce a bill designed to pay for transportation investments through repatriation of foreign income.

Environment and Public Works Chairman James M. Inhofe, R-Okla., consistently ranks among the most conservative senators, but he is quite open about his support for funding infrastructure.

Export-Import Bank The charter for the Export-Import Bank of the United States secured a short-term reauthorization last year that sets up a June 30 deadline for continuing the bank's operation. It's derided by many Republicans as "crony capitalism," but at least one Senate GOP presidential prospect has been vocal in his support.

Sen. Lindsey Graham, R-S.C., held an official event while on a recent campaign-style swing through New Hampshire with Granite State GOP Sen. Kelly Ayotte, touting the importance of Ex-Im financing to small suppliers like the ball-bearing factory they toured. The aerospace giant Boeing is a major beneficiary of the bank, and it has a large manufacturing presence in Graham's state, which also happens to host a key presidential primary.

Supreme Court The Supreme Court's upcoming King v. Burwell decision, regarding the constitutionality of some subsidies through the Affordable Care Act, is likely to create 2016 fodder regardless of which way it lands. Republicans on both sides of the Rotunda have been working on a plan if the high court upends the ability of people who get their insurance through federally operated insurance exchanges to federal subsidies.

But any solution viewed by the GOP base as supporting the law might well generate protests, particularly from senators seeking the presidency. That could particularly be true if a fix were advanced through budget reconciliation, essentially denying conservatives the one chance they have to get a full repeal of Obamacare to the president's desk.

The Supreme Court also is considering challenges related to same-sex marriages, though it is unclear what action Congress might take if the court determines gay marriage should be permitted nationwide, or even that marriages consummated in one state must be honored in another.

Sen. Ted Cruz, R-Texas, has introduced the State Marriage Defense Act, a bill designed to allow states to set their own parameters for defining marriages within their borders.

Funding the Government, Raising the Debt Limit Lawmakers will once again have to complete two of the most fundamental functions of government and this time, Republicans will be responsible on the Senate side for ensuring the statutory limit on the public debt is either raised or suspended.

It's an unpopular vote that's nonetheless necessary to avert default, though conservatives argue debt service payments could be prioritized. After Congress went through this exercise in 2014, Cruz lambasted his GOP colleagues for caving.

"I recently had my staff print out a list of three pages of Republican senators — I might note all the people that are running around the press saying nasty things about me — saying, 'We will stand on the debt ceiling and fight for it,'" Cruz said on Mark Levin's radio program. "And then a few months later, it's like they think the American people are just a bunch of rubes, that we don’t remember what they say,"

In addition to the debt limit, Congress also needs to keep the government funded past Sept. 30. The fiscal 2016 appropriations process is set to get underway in earnest shortly after House and Senate Republicans reach agreement on a budget resolution, and while Majority Leader Mitch McConnell, R-Ky., has made moving spending bills across the floor a priority, it is too early to know if any of the standalone measures can be finalized before Oct. 1, particularly with a Democratic president in the White House.

Authorization for Use of Military Force There is no deadline attached to a fresh AUMF that would replace the George W. Bush-era authorizations for the Afghanistan and Iraq wars and update them for taking on the Islamic State group or military activity elsewhere. But the longer any debate on military forces in the Middle East goes on, and the further away from the original authorizations the country gets, the issue might find itself on the 2016 campaign trail, if not the Senate floor.